Chemoattractant gradients measurement

Bacteria sense spatial gradients of chemoattractants by measurements separated in time. A bacterium sets off in a random direction and, if the concentration of the chemoattractant has increased after the bacterium has been swimming for a period of time, the likelihood of tumbling decreases and the bacterium continues in roughly the same direction. If the concentration has decreased, the tumbling frequency increases and the bacterium tests other random directions. The... 

Gel invasion assays IVacking the paths taken by indiviciual cells Three-dimensional gels are produced with defined chemoattractant gradients, and individual cell movement is measured in all three dimensions. Single cell parameters S and P can be calculated. [117, 148. 151, 247]... 

Under agarose. This assay was originally developed to study leukocyte migration (Nelson et al., 1975) however, it has also been applied to the study of chemotactic and chemokinetic effects of FGF on endothelial cells (Stokes et al., 1990). Cells are allowed to migrate under an agarose gel in which a chemoattractant (or a control solution) forms a diffusion gradient. The differential migration of cells toward the chemoattractant is taken as a measure of its chemotactic activity. 

Microfluidic experiments have shown that it is possible to quantify population-scale transport parameters (chemotactic sensitivity and random motility) of a population of bacteria. Traditionally, transport parameters have been theoretically derived from single-cell behaviour using probabilistic models. But, with a microfluidic capillary it is possible to generate and measure gradients of chemoattractant (a-methylaspartate) while simultaneously capturing the swimming... 

Measurements from the in vivo invasion assay have been shown to correlate with the metastatic properties of cancer cells in a xenograft model of breast cancer, with more metastatic cells invading 15-fold more efficiently than less metastatic cancer cells in response to an EGF gradient, correlating with their in vitro chemotactic responses to EGF (10). Transgenic models of breast cancer have also been examined, and the invasiveness of breast cancer cells to chemoattractants such as TGF-a and heregulin among others was evaluated in the polyoma Middle T model (11). 

Nonmotile neutrophils have a spherical morphology. Within a few minutes of activation with a chemoattractant (either in a gradient or in a uniform concentration), they develop the characteristic polar morphology of a lamellipodium at one end and a uropod at the other. This polarization is a prerequisite for migration of leukocytes, and thus measures of cell polarization are often used as indicators of migration [125, 170]. 

Like population assays, single cell movement has also been measured in three-dimensional gel invasion assays [117,148, 247, 296]. These gels can be constructed such that the chemoattractant concentration gradients are well defined [151, 247]. 

In this assay, the spermatozoa in the well are suspended in a solution containing the chemoattractant. The capillary, containing either a control buffer or the chemoattractant, is immersed in the sperm suspension. When the capillary contains buffer only, the spermatozoa sense a descending gradient of the chemoattractant as they move from the well to the capillary (Figure 7). When the chemoattractant is in both the capillary and the well, they sense no gradient at all. A comparison is made between these two conditions. This assay thus measures the sperm tendency to leave the chemoattractant rather than to accumulate in it. In the case of sperm chemotaxis, sperm accumulation in the capillary is... 

Although this assay measures the main feature of CKRs (i.e., chemotaxis), it does not resemble the in vivo situation. For example, the chemokines do not form a gradient in the lower compartment. Furthermore, the chemoattractants diffuse to the upper compartment in time, which ceases cell... 

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